Cell Growth and Replication

Why Do Cells Divide Instead of Just Growing Bigger and Bigger? The cell's DNA would no longer be able to serve the increasing needs of the growing cell. The cell has more trouble moving enough nutrients and wastes across the cell membrane. Larger cells have a smaller ratio of surface area to volume.

Prokaryotic vs. Eukaryotic Prokaryotic Cell Division: Simple matter of separating the contents of the cell into two parts. Eukaryotic Cell Division: Cell Cycle

Eukaryotic DNA Prokaryotic DNA Located in the nucleus in the form of chromatin/ chromosomes located in the cytoplasm Have a single circular DNA molecule (usually referred to as the cell's chromosome)

Eukaryotic Cell Cycle Cell Cycle - Series of events that cells go through as they grow and replicate. Interphase - Period of the cell cycle between cell divisions (consists of S, G1, and G2 phase) M Phase –Mitosis (division of the cell nucleus) Cytokinesis (division of the cytoplasm)

Cell Cycle- Interphase G1 Phase – Period of intense growth before DNA replication S Phase – DNA (chromosome) replication takes place, still little cell growth G2 Phase – Period of more growth and final preparations before cell starts dividing.

G1 = making the key decision of whether the cell should divide, delay division, or enter a resting stage. G0 = resting stage (Liver cells, for instance, enter mitosis only around twice a year.) The G1 checkpoint is where eukaryotes typically arrest the cell cycle if environmental conditions make cell division impossible or if the cell passes into G0 for an extended period. In animal cells, the G1 phase checkpoint is called the restriction point There are 3 “checkpoints” that allow the cells to continue moving through the cell cycle.

What do all of these have in common? growth from an infant to an adult 2) repairing or replacing damaged issues/organs 3) cancer

Is Mitosis Asexual or Sexual?!??

Asexual Reproduction = Mitosis Asexual Reproduction - Reproduction of genetically identical cells to the parent cell without the fusion of gametes; not necessary to have two parents Examples include: Single-celled organisms Source of new cells when a multicellular organism grows and develops (skin cell, liver cell)

Four Phases of Mitosis Prophase - Chromosomes visible/centrioles; nuclear envelope disappears Metaphase – Centriole go to opposite ends of the cell; spindle fibers emerge from the centrioles; chromosomes line up in middle of cell Anaphase - Sister chromatids are pulled to opposite ends of cell Telophase - Chromosomes condense back to chromatin and nuclear envelope reappears (The four phases are followed by Cytokinesis)

Four Phases of Mitosis

Cytokinesis Usually occurs at the same time as telophase. Cytokinesis - The division of the cytoplasm itself.

Cytokinesis: Plant vs. Animal Cells The cell membrane is pinched into two nearly equal parts = cleavage furrow. Plant Cells: A structure known as the cell plate forms midway between the divided nuclei and gradually develops into a separating membrane. A cell wall then begins to appear in the cell plate.

What Phase Of the Cell Cycle Is It? B C D E F

What Phase Of the Cell Cycle Is It? B C Anaphase D E F

What Phase Of the Cell Cycle Is It? B C Anaphase Telophase D E F

What Phase Of the Cell Cycle Is It? B C Anaphase Telophase Cytokinesis D E F

What Phase Of the Cell Cycle Is It? B C Anaphase Telophase Cytokinesis D E F Interphase

What Phase Of the Cell Cycle Is It? B C Anaphase Telophase Cytokinesis D E F Interphase Metaphase

What Phase Of the Cell Cycle Is It? B C Anaphase Telophase Cytokinesis D E F Interphase Metaphase Prophase

Lets take a deeper look at what DNA is before we learn how it replicates... Deoxyribonucleic Acid (DNA) - The material inside the nucleus that carries all the genetic information Responsible for determining all organism’s traits Eye color, body structure, and cellular enzyme production

The Components of DNA DNA is a long molecule made up of repeating individual units called nucleotides Nucleotides are made up of three parts: Sugar Phosphate Group Nitrogenous Base

Nucleotides Put Together = DNA 3’ 5’ 3’ 5’

Nitrogenous Bases DNA contains four nitrogenous bases: Adenine (A) Guanine (G) Cytosine (C) Thymine (T)

Complimentary Bases [A] = [T] [G] = [C] Chargaff discovered that there were always equal amounts of A & T. And equal amounts of C & G in cells. Adenine pairs with Thymine, and Guanine pairs with Cytosine The complimentary bases are held together by weak hydrogen bonds. (No matter what organism it is!!!!) [A] = [T] [G] = [C]

Purines and Pyrimidines Purines have two rings in their structures. Adenine and guanine belong to this group Pyrimidines have one ring in their structure. Cytosine and thymine belong to this group

Structure of DNA Phosphate Group & Deoxyribose Sugar Nitrogenous Bases Form the backbone or sides of the ladder. Nitrogenous Bases Form the “rungs” of the ladder or middle of the molecule.

The Shape of DNA DNA looks like a “twisted ladder” called a Double Helix.

Discovering DNA Rosalind Franklin - Used X-ray diffraction; Showed the X-shaped pattern of DNA (helix shape) Watson and Crick – Two scientists that discovered the double helix shape in 1953

Chromosome Genes Long, continuous single piece of DNA, contains many genes Sequence of DNA that codes for a protein and thus determines a trait

Chromosomes In eukaryotic cells, the genetic information that is passed on from one generation of cells to the next is carried by chromosomes. The cells of every organism have a specific number of chromosomes The cells of fruit flies have 8 chromosomes. Human cells have 46 chromosomes. Carrot cells have 18 chromosomes.

Chromosomes Well before cell division, each chromosome is replicated, or copied.

Chromosomes Each chromosome consists of two identical “sister” chromatids. When the cell divides, the “sister” chromatids separate from each other. One chromatid goes to each of the two new cells.

Chromosomes Each pair of chromatids is attached at an area called the centromere.

Chromosome Structure DNA molecules are surprisingly long The chromosome of the prokaryote E. coli, which can live in the human colon, contains 4,639,221 base pairs! Analogy: Imagine trying to pack a 300-meter length of rope into your school backpack! DNA must be dramatically folded and tightly packed to fit within the cell

Cell Cycle- Interphase G1 Phase – Period of intense growth before DNA replication S Phase – DNA (chromosome) replication takes place, still little cell growth G2 Phase – Period of more growth ; organelles replicate; final preparations before cell starts dividing.

Cell Cycle – M Phase (cell division) Cell Division - The process by which a cell divides into two new “daughter” cells. M Phase –Mitosis (division of the cell nucleus) Cytokinesis (division of the cytoplasm) Before cell division occurs, the cell replicates, or copies, all of its DNA. Each daughter cell gets one complete set of genetic information.

What does the DNA look like?   CHROMATIN CHROMOSOMES What does the DNA look like? Present in what stage of the cell cycle?

Interphase Cell Divison (M Phase)   CHROMATIN CHROMOSOMES What does the DNA look like? Present in what stage of the cell cycle? Interphase Cell Divison (M Phase)

DNA Replication Before a cell divides, it duplicates its DNA via a process called DNA Replication During the S phase of cell division Ensures that each resulting cell will have a complete set of DNA molecules Result: Two identical DNA molecules (each DNA molecule has one original strand and one new strand)

How DNA Replication Occurs Step 1: Helicase, an enzyme, “unzips” the DNA molecule Hydrogen bonds between the base pairs are broken Result = 2 separated strands of DNA

How DNA Replication Occurs Step 2: A replication fork is formed.

How DNA Replication Occurs Step 3: Free floating nucleotides pair up with complimentary bases Each strand of DNA serves as a template, or model, for the new strand DNA Polymerase – Enzyme that joins individual nucleotides to produce a DNA molecule and also “proofreads” each new DNA strand

You Try It! What is the complimentary DNA strand if the original DNA strand is AGTCTA?

You Try It! Complimentary Strand: TCAGAT What is the complimentary DNA strand if the original DNA strand is AGTCTA? Original Strand: AGTCTA Complimentary Strand: TCAGAT

If a meerkat’s parent skin cell contained 34 chromosomes; after cell division how many chromosomes would each of the meerkat’s daughter skin cells contain? 17 chromosomes 34 chromosomes 68 chromosomes None because skin cells don’t go through cell division

If a meerkat’s parent skin cell contained 34 chromosomes; after cell division how many chromosomes would each of the meerkat’s daughter skin cells contain? 17 chromosomes 34 chromosomes 68 chromosomes None because skin cells don’t go through cell division Asexual reproduction produces cells that are genetically identical to their parents for reasons of growth, repair and replacement.

Regulating the Cell Cycle Not all cells move through the cell cycle at the same rate. Cell growth and cell division are controlled. Cyclins are proteins that regulate the timing of the cell cycle in eukaryotic cells. G1 – 0-5 hrs S – 6-8 hrs G2 – 2-5 hrs Mitosis – 1 hr

Regulating the Cell Cycle If cells are placed in a petri dish containing food: Cells will grow until they come in contact with other cells then they stop growing. If cells are removed from the center of the dish: The cells bordering the open space will begin dividing until they have filled the empty space.

Regulating the Cell Cycle This occurs in an injury as well: If a cut in the skin or a break in a bone occurs, cells at the edges of the injury are stimulated to divide rapidly. When the healing process nears completion, the rate of cell division slows down.

Cancer Cancer - Disorder in which some of the body's own cells lose the ability to control growth. Cancer cell divide uncontrollably and form masses of cells (tumors) Cancer cells may spread throughout the body: Disrupts normal activities and causes serious medical problems or even death

There are many reasons that cells can divide and grow out of control: There are many reasons that cells can divide and grow out of control: * exposure to environmental causes (such as carcinogens or ultraviolet (UV) radiation from the sun) *nutritional deficiencies * genetic causes *some infections (All of these will result in DNA mutations)